1. Field of the Invention
The present invention relates to a home agent of a mobile IP system.
2. Description of the Related Art
A home agent has a function for managing the care-of address (COA) indicating the present position of a mobile terminal (mobile node, MN), intercepting a packet transmitted from any other device to the mobile node, and transferring the packet to the care-of address of the mobile node. Therefore, the aforesaid other device can communicate with the mobile node merely by transmitting the packet to the home address indicating the initial registration address of the mobile node without recognizing the movement of the mobile node.
The care-of address in a home agent is managed by receiving and analyzing a position information notification packet (binding update packet) which is periodically transmitted from the mobile node. Naturally, this information differs for each mobile node, and not only the information is periodically transmitted, but also does it generate every time the mobile node moves, so the amount of information to be processed is enormous. Various kinds of terminals and a personal computer, for example, a PDA having a mobile function, a mobile IP telephone can be considered as the mobile node.
FIG. 1A shows the system configuration of a conventional home agent. A conventional home agent 213 is connected to an external network 211 via a HUB 212, as shown in FIG. 1A.
FIG. 1B is a block diagram showing the configuration of a conventional home agent. In FIG. 1B, the conventional home agent 213 comprises a packet transmission-receiving unit 214 transmitting and receiving a packet, various kinds of IO units 215, a HD 216 storing various kinds of programs for performing necessary processing, a packet processing control unit 217 in which packet processing is realized by loading and executing the stored programs, a memory unit 219 retaining a binding cache table 218.
The home agent shown in FIGS. 1A and 1B is built based on, for example, the contents described in non-patent document 1 shown below.
Non-patent document 1: “A Detailed Explanation of Internet Access from IP Mobile Nodes” Chapter 4, edited by James D. Solomon.
Home agents which generally exist today realize their function by having software such as KAME (http://www.kame.net) and USAGI (http://www.linux-ipv6.org/) installed onto a server device. Said software performs not only the process of managing the care-of address, but also the process of transferring a packet to the care-of address. When it is taken into consideration that the number of the registration addresses is tremendously enormous for one home agent, the amount of information to be processed is also enormous.
Most of the processing time is used for the position information processing for the position information notification packet transmitted from a mobile node. Particularly, when the process of transferring a packet to the care-of address is executed by the hardware which is inserted into an extended slot of a server system, not by the software, the processing amount of transfer to the care-of address which the hardware can process at a time is so huge that the ratio of the processing time used for the position information processing to the whole processing time is all the more high, thus causing the whole processing time to be further extended.
The fact that the home agent has a function for intercepting a packet to a mobile node and transferring the packet to a care-of address means that the home agent must be installed in the position where the packet is freely flowing so that the packet to the mobile node can be intercepted. However, in case the care-of address is altered by a malicious user, the packet to the mobile node is easily captured by him, so it is necessary to raise, particularly, the security level of the care-of address management function of the home agent. In other words, although a home agent must be installed in the place where general users can freely access it, its care-of address management function must be protected from malicious users.
As a recovery procedure to be used when a fault occurs to a home agent, the method of Dynamic Home Agent Address Discovery is stipulated in the IETF-Draft. In this method, when a mobile node detects a fault of the home agent, another home agent is retrieved; a position information notification packet is transmitted to the retrieved alternative home agent; the alternative home page analyzes and sets the position information notification packet; after then, the packet is transferred to a care-of address.
However, there is a problem in that as is apparent from the fact that the detection of a fault of the home agent by the mobile node works as a trigger, this recovery procedure is not carried out without interruption, and there is a problem that a lot of time is taken for the recovery. Moreover, since switching processing is executed via the mobile node, namely under the initiative of a user, it is a prerequisite that the mobile node which the user has must have a fault detection function. Therefore, the home agent itself cannot be said to have a recovery function.